Bug 2543512 (CVE-2026-102830)

Summary: CVE-2026-102830 jupyterlab: jupyterlite-core: JupyterLab: Arbitrary code execution via crafted language pack
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rjohnson
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in JupyterLab. Incomplete validation of language pack headers allows arbitrary JavaScript code to be injected and executed during string translation. An attacker could exploit this flaw by enticing a user to load a malicious third-party language pack, resulting in code execution within the authenticated user's session. This allows an attacker to interact with exposed server application programming interfaces (APIs) to read or modify files and execute commands.
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Description OSIDB Bzimport 2026-09-29 19:01:43 UTC 
JupyterLab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. From JupyterLab 3.0.0 until 4.5.11 and 4.6.4, and in JupyterLite Core 0.8.3 and earlier, the Plural-Forms header in a selected third-party language pack can append JavaScript after a valid plural rule because prefix-only regular-expression validation accepts a matching prefix without requiring the entire header to match. JupyterLab passes the accepted expression to new Function, so loading the catalogue and translating a plural string executes the appended code in the authenticated JupyterLab origin. Where Jupyter Server kernels, terminals, and APIs are exposed, the code can use authenticated server APIs to read or modify files and run code. Impact is much more limited in JupyterLite because it typically lacks most exposed Jupyter Server surfaces. The default English locale is unaffected because it does not load a translation catalogue. This issue is fixed in JupyterLab 4.5.11 and 4.6.4 and JupyterLite Core 0.8.4.